A boiler combusts fuel to heat water and produce steam. Fuel gas is supplied from a fuel supply source to a burner disposed in a gas-fired boiler through a duct, and a decompression device is disposed in the duct to adjust a fuel-supply pressure to the burner.
Patent Document 1 discloses a decompression device applied to a liquid-transfer duct. This decompression device has an uneven section with a wavy cross section formed on an inner wall of a duct forming a flow passage, and a plurality of sheets of mesh metal disposed entirely over a transverse plane inside the duct.
Patent Document 2 discloses a decompression device including a plurality of stages of perforated orifice plates disposed in a flow direction in a flow passage, and mesh-shaped porous metal disposed between the perforated orifice plates. The apertures on the perforated orifice plates have a diameter increasing toward downstream stages, and each aperture is disposed so that apertures on the next stage are invisible when seen from an upstream side toward a downstream side.